1. Field of the Invention
The present invention relates generally to valve bags and, more specifically to a mechanism for sealing a valve bag used to contain and transport fine granular products (e.g., rice hull ash) to prevent loss of the products from the valve bag during the handling and shipping of filled valve bags.
2. Description of the Related Art
Plastic valve bags are multi-walled sacks made of a flexible plastic material. Typically, valve bags are formed by cutting and overlapping each layer of plastic along its length. The overlapping region on the long side of the bag is heat sealed, as well as the short sides or ends; provided that a portion of the long side is left unsealed close to one end of the bag to provide a fill hole or valve channel. Alternatively, the valve channel may be configured along the short side of the bag.
Valve bags are filled through a filling tube inserted into the valve channel. Once the valve bag is filled, the bag is upended so that the weight of the filling material closes the valve channel. However, some of the filling material escapes through the unsealed valve channel whenever the valve sack is being handled. For example, the filling material will seep out of the unsealed valve channel during transport so that the filling material is deposited between the layers of bags in a container. When the consumer seeks to remove the filled valve bags from the shipping container, the loose filling material gets into workers' eyes generating a source of eye irritation. To prevent worker health problems and lost time due to eye irritation, a number of attempts have been made to find a suitable sealing mechanism for valve bags to prevent the sieving or leakage of the bag contents back through the valve channel after filling. Typically, these mechanisms have included coating the inner surfaces of the overlapping valve channel with an adhesive or other sealing material, which may be activated by heat or ultrasonic means. Recently, attempts have been made to construct a valve bag sleeve such as described in U.S. Pat. No. 6,164,823 or a self-closing bag such as described in U.S. Pat. No. 6,126,316 to address this problem.
Although some of the sieving problems have been prevented by these various sealing methods, the current sealing mechanisms are not effective in a number of situations or are inapplicable to many mechanical bag-filling systems. Sieving problems are accentuated in the case of filling materials such as rice hull ash.
Harvested paddy rice is subjected to processing operations that remove the rice hulls from the paddy rice. A major use of the separated rice hulls is as a fuel source. Burning rice hulls releases a great deal of energy and renders fine amorphous SiO2 or black dust particles called rice hull ash. These dust particles are primarily composed of silica and contain considerable air space within its interstices, thereby producing a remarkably insulative material often used to insulate molten steel.
Typically, rice hull ash is packaged, sold and transported in plastic valve bags. To date there has been no successful mechanism for sealing valve bags containing rice hull ash during their transport. One problem is that once a bag is filled on the fill tube and is removed, the fill tube drags particles of the rice hull ash along with it across the ends of the valve channel contaminating the opposing surfaces, thereby preventing a tight seal when the adhesive on the opposing surfaces is activated. This is a particular problem if the adhesive is to be activated by heat, since the rice hull ash has particularly strong insulative properties.
Thus, there is an existing need to securely seal a valve bag filled with minute particles having insulative properties. Since filling of the valve bag typically contaminates the sides of the valve channel with the particles with which the valve bag is filled, a protection means is needed that will protect the surfaces of the valve channel during the filling of the bag to ensure the secure sealing of the valve channel once the valve bag has been filled and flattened.